CODEWITHSUNDEEP
pythondeep-copy
Alexander Gruber
Alexander Gruber

Reputation: 519

Referencing where a child object goes using deepcopy in Python

A question about deepcopy in Python:

I have a class A which contains a list of objects from class B, and a class C which contains a list of objects from class A.

class A(object):
    def __init__(S):
        self.S = set(S)

class B(object):
    def __init__(buddies):
        self.buddies = set(buddies)

class C(object):
    def __init__(L):
        self.L = set(L)
    def SplitA(a,b):
        left = deepcopy(a)
        left.S -= new_b.buddies
        right = A(new_b.buddies)
        L |= left
        L |= right

So I want C to have a Split function which, given an A object a and a B object b in a.S, will make two new A objects: one containing the 'buddies' of b (which are in a.S), one containing of the rest of a.S.

The problem is, I don't know how to figure out what the designated b becomes in the deepcopy. In other words,

how do I find new_b in the above code?

(Note: In my actual code it is important to do it in this order, i.e. adding new_a and then splitting a into left and right would not work.)

Upvotes: 1

Views: 236

Answers (2)

Jonathan
Jonathan

Reputation: 2845

This code should do what you were looking for.

from copy import deepcopy


class A(object):
    def __init__(self, S):
        self.S = set(S)


class B(object):
    def __init__(self, buddies):
        self.buddies = set(buddies)


class C(object):
    def __init__(self, L):
        self.L = set(L)

    def SplitA(self, a, b):
        left = set()
        left -= b.buddies   # Since the objects in the sets are unchanged
                            # you can do a set difference that will leave you
                            # with only the members of a that are not in b
        left = deepcopy(left)  # Now get a deep copy of left
        right = deepcopy(b.S)  # and a deep copy of b.S
        self.L |= left      # and combine them
        self.L |= right

Upvotes: 0

Steve Barnes
Steve Barnes

Reputation: 28390

The answer is that the designated b does not become anything other than b in deep copy as you are not deep copying b at all. So just replace new_b with b in your example.

Upvotes: 1

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